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Security Advisory CERT-NL
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Author/Source : Xander Jansen Index : S-98-72
Distribution : World Page : 1
Classification: External Version: 1
Subject : FreeBSD IP fragmentation denial of service Date : 6-Nov-98
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By courtesy of FreeBSD inc. we received the following information.
FreeBSD inc. Advisory SA-98:08 reports a vulnerability regarding
to IP fragmentation denial of service.
CERT-NL recommends implementing the solution outlined in section V.
=============================================================================
FreeBSD-SA-98:08 Security Advisory
FreeBSD, Inc.
Topic: IP fragmentation denial of service
Category: core
Module: kernel
Announced: 1998-11-04
Affects: FreeBSD 3.0 and
FreeBSD-current before the correction date.
Corrected: FreeBSD-3.0 and FreeBSD-current as of 1998/10/27
FreeBSD only: Yes
Patches: ftp://ftp.freebsd.org/pub/FreeBSD/CERT/patches/SA-98:08/
I. Background
IP connections are controlled through a series of packets that are
received by the two computers involved in the connection.
When packets are too large to be sent in a single IP packet (due to
interface hardware limitations for example), they can be fragmented
(unless prohibited by the Don't Fragment flag).
The final destination will reassemble all the fragments of an IP packet
and pass it to higher protocol layers (like TCP or UDP).
II. Problem Description
There is a bug in the IP fragment reassembly code that might lead
to a kernel panic. An attacker can create and send a pair of
malformed IP packets which are then reassembled into an invalid
UDP datagram. Such an UDP datagram would then cause a server to
panic and crash.
III. Impact
When this bug is exploited the operating system will panic. This results
in a reboot of the system.
This vulnerability has been discussed in public security forums and
exploit programs are circulating to take advantage of this bug.
IV. Workaround
None.
V. Solution
Index: ip_input.c
===================================================================
RCS file: /home/cvsup/freebsd/CVS/src/sys/netinet/ip_input.c,v
retrieving revision 1.102
retrieving revision 1.103
diff -u -u -r1.102 -r1.103
--- ip_input.c 1998/10/16 03:55:01 1.102
+++ ip_input.c 1998/10/27 09:11:41 1.103
@@ -750,7 +750,7 @@
* if they are completely covered, dequeue them.
*/
for (; q != NULL && ip->ip_off + ip->ip_len > GETIP(q)->ip_off;
- p = q, q = nq) {
+ q = nq) {
i = (ip->ip_off + ip->ip_len) -
GETIP(q)->ip_off;
if (i < GETIP(q)->ip_len) {
=============================================================================
FreeBSD, Inc.
Web Site: http://www.freebsd.org/
Confidential contacts: security-officer@freebsd.org
Security notifications: security-notifications@freebsd.org
Security public discussion: freebsd-security@freebsd.org
PGP Key: ftp://ftp.freebsd.org/pub/FreeBSD/CERT/public_key.asc
Notice: Any patches in this document may not apply cleanly due to
modifications caused by digital signature or mailer software.
Please reference the URL listed at the top of this document
for original copies of all patches if necessary.
=============================================================================
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CERT-NL is the Computer Emergency Response Team for SURFnet customers.
SURFnet is the Dutch network for educational, research and related institutes.
CERT-NL is a member of the Forum of Incident Response and Security Teams
(FIRST).
All CERT-NL material is available under:
http://www.surfnet.nl/surfnet/security/cert-nl.html
ftp://ftp.surfnet.nl/surfnet/net-security
In case of computer or network security problems please contact your
local CERT/security-team or CERT-NL (if your institute is NOT a SURFnet
customer please address the appropriate (local) CERT/security-team).
CERT-NL is one/two hour(s) ahead of UTC (GMT) in winter/summer,
i.e. UTC+0100 in winter and UTC+0200 in summer (DST).
Email: cert-nl@surfnet.nl ATTENDED REGULARLY ALL DAYS
Phone: +31 302 305 305 BUSINESS HOURS ONLY
Fax: +31 302 305 329 BUSINESS HOURS ONLY
Snailmail: SURFnet bv
Attn. CERT-NL
P.O. Box 19035
NL - 3501 DA UTRECHT
The Netherlands
NOODGEVALLEN: 06 52 87 92 82 ALTIJD BEREIKBAAR
EMERGENCIES : +31 6 52 87 92 82 ATTENDED AT ALL TIMES
CERT-NL'S EMERGENCY PHONENUMBER IS ONLY TO BE USED IN CASE OF EMERGENCIES:
THE SURFNET HELPDESK OPERATING THE EMERGENCY NUMBER HAS A *FIXED*
PROCEDURE FOR DEALING WITH YOUR ALERT AND WILL IN REGULAR CASES RELAY IT
TO CERT-NL IN AN APPROPRIATE MANNER. CERT-NL WILL THEN CONTACT YOU.
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